As is known in the art, a light source or lamp generally refers to an electrically powered man made element which produces light having a predetermined color such as a white or a near white. Light sources may be provided, for example, as incandescent light sources, fluorescent light sources and high-intensity discharge (HID) light sources such as mercury vapor, metal halide, high-pressure sodium and low-pressure sodium light sources.
As is also known, fluorescent and HID light sources are driven by a ballast. A ballast is a device which by means of inductance, capacitance or resistance, singly or in combination, limits a current provided to a light source such as a fluorescent or a high intensity discharge light source, for example. The ballast provides an amount of current required for proper lamp operation. Also, in some applications, the ballast may provide a required starting voltage and current. In the case of so-called rapid start lamps, the ballast heats a cathode of the lamp prior to providing a strike voltage to the lamp.
As is also known, a relatively common ballast is a so-called magnetic or inductive ballast. A magnetic ballast refers to any ballast which includes a magnetic element such as a laminated, iron core or an inductor. Magnetic ballasts are typically reliable and relatively inexpensive and drive lamps coupled thereto with a signal having a relatively low frequency. One problem with magnetic ballasts, however, is that the relatively low frequency drive signal which they provide results in a relatively inefficient lighting system. Furthermore, magnetic ballasts tend to incur substantial heat losses which further lowers the efficiency of lighting systems utilizing a low frequency magnetic ballast.
In addition to efficiency, it is desirable, in some applications, to provide an instant-start lamp capability. Instant-start capability refers to the capability of starting a lamp within 50 milli-seconds (msec) of the time a strike voltage is provided to the lamp. To accomplish this, the ballast must provide a strike voltage typically in the range of about 500 V RMS. Magnetic ballasts are unable to produce a strike voltage which is large enough to cause the lamp to operate in an instant-start mode.
In an attempt to overcome the low efficiency problem caused by the low frequency operating characteristic of magnetic ballasts as well as the inability to operate in an instant-start mode, attempts have been made to replace magnetic ballasts with electronic ballasts. Electronic ballasts drive the lamps with relatively high frequency drive signals and can provide strike voltages which allow instant-start lamp operation. One problem with electronic ballasts, however, is that they, however, utilize a relatively large number of circuit components which reduces reliability and maintainability of the electronic ballast while increasing cost of the ballast.
Furthermore, in a lighting unit which includes a light source, a reflector, a housing and a magnetic ballast, it is relatively expensive to replace the magnetic ballast with an electronic ballast. This is due, at least in part, to the costs associated with the electronic ballast itself as well as the cost of labor required to physically disconnect the magnetic ballast from the lamp and electrically connect the electronic ballast to the lamp. Furthermore, some ballasts include a potting material which may include hazardous materials such as PCBs and asbestos. It is necessary to dispose of such hazardous waste materials in a particular manner and such disposal costs are significant.
It would therefore, be desirable to provide a relatively inexpensive circuit which allows a magnetic ballast to provide high frequency operation of a light source and which is relatively easy and inexpensive to couple to existing light units which utilize magnetic ballasts.